Chromium-plated worm shaft



April s, 1930. A. www@ 4 1,753,773

CHROMIUM BLATED WORM SHAFT Filed oct. 1, 19.26-

In/manto@ Patented Apr. 8, 1930 ALBERT CHAMPION, F FLINT, MICHIGAN,

PATENT OFFICE.

ASSIGNOIL TO A C SPARK PLUG COMPANY,

0F FLINT, MICHIGAN, A CCMPANY 0F MICHIGAN CHROMIUM-PLATED 'WORM SHAFT Application led October 1,v 1926. Serial No. 138,940.

The invention relates to a drive shaft construction which, while in some respects of more general application, has been especially designed for, and will be herein described as applied to, the driving mechanism of a magnetic speedometer. The object of the invention is to provide means for reducing friction between engagin metal parts and thereby to increase their durability, also to practically eliminate the losses in such parts as hitherto produced due to distortion resulting from the usual processes of hardening.

In the manufacture of steel shafts, gears and the like, in accordance with usual practice, it has been customary to machine the article to the desired formthen to subject it to suitable heat treatment to produce the hardened surface necessary to provide for resistance to wear. This treatment results in more or less distortion of the articles so that a large percentage, amounting in some cases to morey than 50%, had to be discarded. In accordance with the present invention I machine the partin the usual manner and then provide a hardened surface thereon by coating with chromium, thus wholly eliminating the step of heat-treatment together with the attendant waste, and with greatly superior results as to durability and reduced friction.

Another difficulty has hitherto been encountered in the use of steel parts mounted in bearings of certain alloys which have a ten, dency to adhere to or alloy with the steel under the influence of friction. This effect is particularly noticeable in the use of mechanism where steel parts engage with parts composed of zinc base alloys such as are commonly employed for die-casting. This diicultyIhave found can be avoided by applying chromium to the surfaceof the steel part which contacts with the alloy metal. The chromium seems to have no affinity for the softer metal and acts in engagement with the alloy almost as if it were a lubricant. By the use of the chromium coating Iiind it possible to form bearings for the steel directly in the alloy metal and still avoid any attack of the zinc upon the steel such as has hitherto occasioned the roughening of the steel and resultant rapid wear of the bearing.

lIn the accompanying drawing showing one embodiment of the invention, Figure 1 is a vertical section throu h a portion of a speedometer and Figure 2 1s a longitudinal section showing the drive shaft of the speedometer 55 on an enlarged scale.

Referring` to the drawing, 5 indicates a portion of vthe frame of the speedometer. This frame is formed preferably by die-casting from an alloy which contains a large percentage of zinc. Bearings 6 and 7 are formed in the frame to support the drive shaft 8, the latter having journals 9, 10, arranged to rotate respectively in the bearings 6, 7. At one end the shaft maymbe provided with means, as the squared portion v12, for engagement with any suitable coupling. At the other end is a worm 13, constituting preferably an integral part of the shaft, and arranged to engage a Worm wheel 14,fwhich may be a part of an odometer mechanism. An armature 15 may be secured to the end of the shaft to be rotated thereby. The worm Wheel 14 as well as the shaft 5 and worm 13 are preferably of steel for strength and cheapness.` To reduce the Wear between the -steel parts, however, and to eliminate the tendency of the steel journals to become alloyed with the metals of the frame, I coat the shaft and worm with chromium. This 30 coating is applied preferably by electrodepo- Y sition and may be of very slight thickness. In practice I find that the chromium layer between the steel parts and between the steel and alloy part-s reduces the adhesion or friction and interaction of one metal upon another to such an extent that Jwear is substantially negligible throughout the normal life of the instrument.

While I have herein described by way of illustration a specific embodiment of the in-- vention I do not desire to be restricted thereto except as required by the terms of the annexed claims in view ofthe prior art.

I claim:

1. The combination with two parts having frictional engagement with'each other, one of said parts having an ingredient tending to alloy with the other, but not with 4chro- 100 mium, under the influence of friction, of a coating of chromiumI on one of said parts.

2. The combination with a frame contain.- ing zinc, of a steel shaft journalied in said frame and a coatin of chromium on the journals of said sha 3. In a speedometer, the combination of a frame, a worm wheel, said frame being of die-cast metal having a zinc base, a shaft journaled in said frame and having a Worm thereon engaging with said Worm wheel, and a coating of metallic chromium on the journal portions and the worm wheel portions of said shaft.

In testimony whereof I aiiix my signature.v

ALBERT CHAMPION. 

